First of All Before Anything Make Sure you Have Enough Storage from Settings -> Storage Then Check How Much
Free Storage do you Have ? At least You Should Have Between 15GB -> 50GB Free Storage For Roms
On the Top Left of The Rom Icom You will Find
After You Click on The Icon It Will Open a Menu
Click on Modify Then Choose ISO File Section
After you Click on it Choose the ISO File You Want to Import
Then Wait till it Fully Imported
and Run the Rom then Check the D:/ Drive if the ISO File have been Imported Successfully or Not