Sounds odd, but not impossible ;)
I don't know about merge requests via email, sounds weird... maybe you have to make a clone of tiki to make an MR from first? Personally i've never got the hang of them, so not sure i can help more, maybe we can get a proper git export here to help?
I presume you read https://dev.tiki.org/Git-Workflow which supposedly is the "how to" page?
Also, it would be good if you joined the dev mailing list here, which is where most developer discussion happens, often about how to make git work!
Thanks for trying!