The only way to make use of airtime you bought by mistake from equity bank or KCB is to find online businesses that buy airtime in bulk. Such businesses will buy your airtime at a rate of 70%.
For example, if you send them airtime worth Ksh. 1000, they will give you Ksh. 700. Do a Google search and you will find them.
There is no other way of reversing airtime purchased from equity bank through app or USSD code.