should i set the game to high performance mode

i have an alienware 17 r5 laptop which has switchable graphics which are nvidia geforce gtx 1080 and intel card

when i play some games i will get the geforce overlay popup in the upper right telling me to press alt and z if i want to use geforce experience in game. the popup shows when i launch the game. if that popup shows then that should mean that the game is using the nvidia card

however in some games there is no overlay popup in the upper right. when that happens i am not sure which graphics card the game uses. some games are stupid and they try to use the intel card and the game will slow down and freeze. that has happened to me before with one game and there was no overlay popup for that game when i launched it. i had to force that game to use the nvidia card by setting the game to high performance mode in the graphics setting which is under display settings in windows and after that the game worked ok

should i always set the game to high performance mode when i dont get the overlay popup when i launch the game just in case the game is stupid and it tries to use my intel card?

Geforce Experience is just an automatic/suggested game setting thing, you really don't need it. Has nothing to do with setting the desired graphics hardware.

Depends on a particular Laptop, and the hardware involved, but look at both of these:
1) Look in the BIOS/UEFI for Graphics Card settings.
2) Look in the Nvidia Control panel > Manage 3D settings > Program Settings > Select program to customise > Select preferred graphics processor.
You may have to add game manually.
Method 2) is for Optimus type of Laptops.