Forefoot varus is an uncommon pathomechanical entity in which the forefoot is inverted on the rearfoot when the subtalar joint is in it defined neutral position and the midtarsal joint is fully pronated. This is the standard textbook definition, but does get warped quite a bit by those with limited understanding of foot biomechanics. As a result the forefoot is inverted relative to the rearfoot so the foot foot has to “overpronate” to get to the ground. Forefoot varus is a bony deformity, whereas the much more common forefoot supinatus is a soft tissue cause of an inverted forefoot. It is the confusion between these two very different types of an inverted forefoot that leads to a lot of bad information about both these pathomechanical entities. More on the differences can be found here.
Forefoot varus causes the foot to ‘overpronate’ as in the above diagram. Whereas, forefoot supinatus is the result of ‘overpronation’. That ‘overpronation’ may or may not result in symptoms from that pronatory compensation, depending on the loads in the tissues (eg supination resistance). There is a lot more here on the distinction between the two.
The only way to treat a forefoot varus is to bring the ground up to the foot with a foot orthotic so that it does not have to pronate the foot to get to the ground. There is no other way to treat forefoot varus. Forefoot varus is a bony problem, so can not be changed.
There is plenty of advice on the web to use muscle exercises, such a the short foot exercise to strengthen the muscles to raise the arch. This is really bad advice for forefoot varus and will not work. It will work for some of the other causes of overpronation, but not this one.