How to specify the directory path on external memory card? An app currently saves files to "mydir" on the internal memory:

/storage/emulated/0/mydir

Instead, I want the files saved onto external memory card, but I am unable to figure out what is the right path. The attempts below do not work:

/SanDisk SD card/mydir

/storage/SanDisk SD card/mydir

/storage/emulated/SanDisk SD card/mydir

Android 9 , Redmi 8

"SanDisk SD card" comes from a file manager app, not sure if the card is to be specified by this or something else.
/storage/36E2-14BB/


this is what stands for the external microSD card,

/storage/36E2-14BB/mydir


...and this is for my own custom directory on the microSD.

(I got the /storage/36E2-14BB/ from an app where the available folder options were listed in a drop-down menu. Otherwise, no clue how to arrive to the 36E2-14BB and it is is unique or universal to each microSD cards.)