There isn't a single passage teaching about the existence of church covenants; rather, the doctrine is built on a number of biblical principles, which include but are not necessarily limited to the following.
1. The Plurality of Local Churches. The term "churches" normally appears in the plural throughout the New Testament when referencing local congregations. There aren't "new covenants" in the plural, but the Bible does speak of "churches" in the plural. These local church bodies in the New Testament are composed of Christians who have voluntarily and mutually agreed to come together for the sake of the gospel, to establish a church, to appoint the New Testament officers of elders and deacons, who are not officers with authority over all the local churches of the new covenant, but only over a specific local church. Local church bodies mutually consent, agree, or covenant to sit under the teaching and ministry of specific officers, to which other local churches have not consented. The decision to appoint certain men as deacons over the Jerusalem church was a proposal that "pleased the whole group" (Acts 6:5). Therefore, the Bible teaches that the local churches are distinct assemblies (plural) composed of specific individuals in which members have mutually agreed (covenanted) to submit to the authority of specific officials.
2. Church Discipline. Each individual local church is responsible to discipline its own membership and does not have authority over the memberships of other local churches. This shows that there are bodies of believers in the New Testament that have covenanted or agreed to walk together in mutual accountability. According to Scripture, the highest court of appeal in matters of discipline is the whole local church body. "If he refuses to listen to them, tell it to the church" (Matt 18:17). The punishment of excommunication was inflicted "by the majority" (2 Cor 2:6-8) at the local church of Corinth. Thus, local churches have mutually consented to submit to the discipline of their own memberships but are not bound to receive discipline from the membership of a sister church. The majority of the members of the church of Corinth was what was required, period. The fact that local churches have the authority to discipline those in their memberships shows that local church members are mutually submitted, or covenanted, to the terms of the new covenant.
3. Distinct from Both Outsiders and Unbelievers. Local churches are composed of a specific group that is recognized as distinct from both outsiders and unbelievers. 1 Corinthians 14:23 speaks of times when the "whole church comes together." It says, “If, therefore, the whole church comes together and all speak in tongues, and outsiders or unbelievers enter, will they not say that you are out of your minds” (1 Cor 14:23)? Note that the text distinguishes "outsiders" and "unbelievers" from the "whole church." It's not simply saying that unbelievers are outsiders or that outsiders are unbelievers, but it's saying first that there are those who are outside the Corinthian church, outside the bounds of its membership, which includes any and all people, believers and unbelievers, who aren't Corinthian church members, and then second the whole local church is distinct from unbelievers. Thus, a local church is a specific, known, recognized group of believers distinct from all outsiders, including non-member believers, and unbelievers.
While the words "church covenant" are never used in the Bible, Scripture represents local churches as involving an agreement or mutual consent among professing Christians to walk together as a local assembly, to walk under the ministry of specific appointed officers, and under the discipline of that local church. That mutual agreement is a covenant.
Thus, there are evidently two covenanted groups in view in the NT. First, there is the local church, which agrees, or covenants to walk together under the terms of the new covenant. And, second there is the new covenant, which includes the whole invisible people of God, believers in all places everywhere.