Can't activate new prepaid phone to replace an existing phone on my account

I purchased Samsung J2 Dash AT&T prepaid phone and am trying to activate the SIM and have this phone replace my existing S4 Mini on my existing regular monthly shared family plan (not prepaid plan). I have done this several times in the past for other lines on my account, but it looks like AT&T does not have this online activation option now for this scenario. I tried selecting Wireless Upgrade and BYOD options but none work for what I'm trying to do. My old phone has the larger micro SIM so I can't just swap the SIMs. Is there any way to do this without having to go to AT&T store which I'm trying to avoid with the COVID virus? I don't want to hang out in the store while they touch my phone. Shouldn't be this difficult to upgrade/replace an existing phone that is not under contract.