A friend and I have been building an app as a little side project for a few years. With work and real-life etc. it's been stuck in beta for quite some time, but we were actually hoping to launch this weekend.

Today we discover that a competitor launched with an identical concept. Fine, it's an obvious concept that I was surprised no-one had come up with already, and we lifted a large part of the UI from Tinder anyway. What I'm concerned about is that they also copied the name (changing one letter: Chowder (https://www.getchowder.com) -> Chowdr (https://www.chowdrapp.com)) and filed a trademark.

Is there prior art for trademarks in the US (we have been publicly visible as Chowder since ~February 2016, it seems their trademark was filed in March 2016)? I was able to find some info about the trademark (https://www.bizapedia.com/trademarks/chowdr-87042422.html) - of note is that they have a pseudo-mark for 'Chowder' as well.

While I'm annoyed that this person lifted the concept and the name, I am more worried that they will make a trademark infringement move on us as soon as we launch properly, which we cannot afford to defend against.

If it makes any difference, we have the option to become a registered company in the UK (where I am based), however we planned to launch in the US initially anyway, so I assume this would still classify as infringement?

Any advice would be appreciated. At this stage I'm thinking we should just rebrand.