Since the root area is reduced, I would reduce the top area also by pruning. Don't let it dry out but don't keep it too wet. They need moist well drained soil.

I think I neglected it as generally I only grow edible plants but will try above and maybe will recover completely

Ruth, growing these long term in containers is pretty specific...

You need a good potting medium, one that is porous but has some water retention...garden centers will often carry a mix called (surprisingly) Azalea Mix. Your greatest responsibility is proper watering - You should never let it dry out, but you can't drown it either. Moist but not soggy.

Unlike azaleas in the ground, you will need to fertilize in your container but in your cold winter climate you may want to stop in mid June. Something formulated for acid loving plants, liquid in form is best - it's easy to burn roots with granulated types. Err on the weak side, and dilute from the label instructions for the product you buy.