Can you select a particular runner to use for a merge request pipeline?

It’s quite possible i’m misunderstanding here, but i’m trying to setup a pipeline for merge requests, but i need to select a particular runner for it to run upon (a runner that’s within the aws environment that’s associated to that of the target branch). I’ve tried putting CI_MERGE_REQUEST_TARGET_BRANCH as a tag on that task but it doesn’t get interpolated apparently.

I did see there’s a feature called ‘pipelines for merged results’ which might (sadly) be what i need ? That’s not available in our subscription plan so i can’t be sure.