how to remove permatex rust treatment?????

i recently used this on a nef r92, i can still see rust underneath the coating. i am worried it didn't stop the rust, i am thinking of a complete tear down and reblue. how would i remove the rust treatment. thanks

i can still see rust under the coating, don't know if it stopped the rust or not. never used it before. don't know nothing about sand blast and no gunsmiths that i know of anywhere near me.