Hi @hankghgold,
If the two images are aligned with each other, then all you would need to do is regrid one image to the other. You could use something like mrgrid (mrgrid — MRtrix 3.0 documentation). But I would be careful in that it sounds like you are either going to lower the resolution of your T1 image by a lot (losing data) or upsample your fmri by a lot (leading to unnecessary data interpolation). Based on your fMRI image resolution, it appears you might have already upsampled your BOLD image unless you were able to acquire it with sub-mm resolution.
Best,
Steven