Switching apple watch-standalone plan to digits plan?

I recently received my Apple Watch SE (2021) from Tmobile that I had ordered on a standalone plan. At the time I believed I would be able to use it alone with its' own number since I chose the standalone plan option. 

However, the iPhone I used to set it up with, is serviced with AT&T. Therefore, I was not able to setup the cellular service with Apple Watch SE from Tmobile because my iPhone is with AT&T. (Note: I did not want to do the “add a family apple watch” as this would cause me to create a new iCloud account)

So, I went ahead and ordered a iPhone with Tmobile. Because I was not expecting to have an iPhone with Tmobile, I would like to switch the Apple Watch to a DIGITs plan instead of a standalone plan. 

Would this be possible?