Certified GKH Gardening Expert
The damage is characteristic of coconut rhinoceros beetle, which will infest banana plants. I am not sure if this pest is prevalent in your locale. It could be another large beetle or weevil. In any case the control measures will be the same.
Sanitation is important to eliminate the habitat for larvae development, which is fallen wood and debris, open compost and manure piles.
It is not possible to repair the damage that has been done, but it is possible to prevent further infestation. For ornamental plants, not food plants, a systemic insecticide applied to the soil for root uptake is effective. And/or a contact and barrier insecticide spray drenched on the foliage and into the leaf bases will work for a period of time, after which it needs to be repeated.
Contact a local tree service with a plant health care division or a landscape pest control company. Professional applicators have access to better insecticide products and know the best timing for effective applications.
For do it yourself organic method and material, you can use a neem oil product with Azadirachtin, (not the less potent 70% neem oil without the Azadirachtin). But you will need to spay the entire plant every two weeks. It's preventive and effective for a wide range of pests, only as a repellent.