changing sims

[TLI_Mark]

I have a CBA850 with dual sims. I have two ATT sims from different accounts in the modem. What is the easiest/fastest/most efficient way to change from Sim1 to Sim2. I have a main scenario and a second.

1) my main interest is making sure neither sim uses more than 1Tb of data in a monthly cycle. I would think I could set Sim1 to automatically switch to Sim2 when it has used 750Gb (for instance). Then go back to Sim 1 at the beginning of the next billing cycle.

2) how do I easily manually force the move from Sim1 to Sim2 (if for some reason I want to manually make the change)

I see the settings that I think will do #1 but it's hard to know if it is set up correctly until data gets used. For #2 I've simply "disabled" the sim I don't want and that forces that change to the other sim, but that seems ineffienct and makes me think there must be a better way that I'm not finding.