If your phone was running something other than "Marshmallow" before, and you had apps running on the card, then I am assuming you had the phone rooted? Most prior versions cannot run apps from an SD card. However Android "Marshmallow", a.k.a. 6.0 actually can. Unless of course it is a device that the manufacturer has restricted this option on. Sadly, it happens.
If the device is rooted, you would need assistance on that, which I cannot give you. If it wasn't rooted, then I would start to wonder what was done to the phone so that you could run apps from a card?
To run them from the SD card in "Marshmallow" would require the card be formatted and encoded to work. That can't be done while anything is on the card as it will wipe the card...