That is a bit of a difficult question to answer, for a start how do you intend to connect the 3rd party router, as an AP on the same subnet in Bridge mode?
What might be a better approach is to investigate the issue that I assume that you have with your Eero & then look for solutions.
The TalkTalk Community has now moved to a peer-to-peer support model. This means that the TalkTalk team will no longer be here to support with queries. Don’t worry, there are plenty of ways to reach out if you need to speak to TalkTalk directly. For more details check out the link here
How to contact TalkTalk Broadband - TalkTalk Help & Support
