Basically, unless your OEM did something very nonstandard, you can't.
Marshmallow has no facility to move apps to the SD card as that feature was removed in favor of adopted storage in the core operating system. In adopted or internal storage mode, the SD card is essentially "adopted" or brought into the internal storage as if it is built into the device. This method is not without drawbacks though, your SD card will become encrypted and can only be read by that device (not in another phone or computer) and it will put significantly more wear on the card which is a concern because SD card storage has a finite number of writes before becoming unusable. Adopted storage is also slower than standard internal storage in general.
Even with adopted storage you don't chose what to move, the operating system does that... And some apps cannot reside on the SD card even with adopted storage.