My partner had a small itchy lump at the middle of his insole for a year. however, there are four lumps now and they are very itchy. what should i do?

See a doctor: Cannot answer this without seeing the problem. He should be examined by a physician.

Probably a wart: Plantar warts (found on the bottom or plantar surface of the foot) can be painful or just it itchy. They can be identified by the presence of small, pinpoint black spots within the "lump" you are describing. Take a close look at them and you may be able to confirm.

Planter Fibromatosi: Is a relatively uncommon non-malignant thickening of the feet's deep connective tissue, or fascia. In the beginning, where nodules or cords start growing along tendons of the foot, the disease is minor, can be painful. Eventually, however, the cords thicken, the toes stiffen and bend, and walking becomes painful. You have to be careful some time fibrosarcarcoma (malignant) but also rare. Check.

Infection Too: In addition to dr hadied's comment, a verruca plantaris can be locally aggressive from auto-inoculation from the original lesion. This is related to viral infection by hpv. Dermatophytoses (fungus) in the form of tinea pedis can have atypical presentation (nodular, as described). Sometimes scratching the lesion can cause this nodular change (prurigo nodularis). See your md/do/dpm for DX and trx.