[{"key":1,"_id":"65be2c18847caa0b4f0000f0","wallets":[{"name":"test1","balance":50},{"name":"test2","balance":100}]},{"key":2,"_id":"65be2c18847caa0b4f0000f1","wallets":[{"name":"test3","balance":70},{"name":"test4","balance":80}]}]

db.collection.update({_id:"65be2c18847caa0b4f0000f0","wallets.name":"test2"},{$inc:{"wallets.$.balance":-20}})