If you have both types of data plans (one from your mobile operator and one from another mobile operator through the Mobile Plans app), you can switch between them at any time. 

Select Start  > Settings  > Network & internet > Cellular to choose a data plan. To use your mobile operator SIM card, select SIM1 for Use this SIM for cellular data. To use the data plan on your eSIM, do one of the following, depending on which Surface with LTE Advanced or 5G model you have:

For Surface Pro with LTE Advanced (5th Gen), select SIM2 for Use the SIM for cellular data.

For all other LTE Advanced or 5G devices, select eSIM for Use this SIM for cellular data.

To learn more about your cellular settings, see Cellular settings in Windows.