This guide works also for Original Prusa MINI/MINI+ smooth PEI steel sheets.
Since these are a little bit smaller, the difference is that after applying a new PEI sheet you have to trim more material from its sides.
The same new uni-size replacement MK3S+ PEI sheet can also be used for older MK2S printer heatbed. Compared to the discontinued MK2S PEI sheet, the MK3S+ PEI is a bit larger and more material has to be trimmed after applying.
After you get the new PEI sheet and all the other necessary materials, please follow the older guide for MK2S printer.