how to fix 4 wheel drive

This is not a simple matter. Go to a Mazda or Ford specialist or a 4WD shop. Here's a directory link for you: https://repairpal.com/mazda-repair-in-woodbury-connecticut

I had to replace the Motorizer on the transfer case. It was stuck in 4 wheel high The brushes were worn out. Actually I found a set of brushes and replaced them. On my ruck if yours is the same year 2000 B400 the motorizer can be removed and you can manually take it out of 4 wheel drive by turning the actuator shaft by hand be careful not to force it.