You can just put it in a hot wash BUT it will probably shrink and harden and not stay lovely and soft.
I would be inclined to unravel and re-knit or if you have any wool left over knit a small square (like the tension test ones you do before using a pattern) and experiment with shrinking that and drying it before you try the whole garment.
Mohair can be made into felt so I would be worried you'll get a felt effect if you try to just heat shrink.
Good luck.