Gaining ankle mobility after a sprain can be challenging.
One technique that we often use is to place some sort of elastic wrap around the front of the ankle joint to provide support and glide to the joint while then performing mobility exercises.
What to use and how to keep in in place are two big challenges to this useful set of exercises. We have found that using a old thin (700cc or road bike type) inner tube works best. This tends to work particularly well if you use a variation of a figure 8 loop around the heel and forefoot to lock the the wrap in place.