How to reset the service interval after an oil change
The order of steps, and an honest answer to why it does not work on every car.
Change the oil first
Resetting the counter is a note in the control unit, not a service. A cleared interval with old oil only means the reminder comes later than it should.
Check the adapter can do it
A reset is a long command to a specific module, not a code read. A cheap ELM327 copy usually cannot manage it: it answers «OK» and delivers nothing to the module. The app checks the adapter beforehand and says plainly what it is capable of.
Switch the ignition on without starting
Most service procedures are done that way. With the engine running, some modules switch to a state in which they refuse writes.
Choose the service interval reset
The app first asks the module whether it supports the procedure and only then offers to run it. If it does not, it says so rather than pretending it worked.
Check the result on the dashboard
Switch the ignition off, wait ten seconds and switch it back on. The counter to the next service should show the full interval. That is the only real confirmation: an «OK» from the adapter is not one.
If it did not work
There are three causes, all honest: the car does not support an OBD-II reset (on some makes it is done with the dashboard buttons only), the adapter cannot carry the long command, or the module answers on a manufacturer protocol an ordinary ELM327 cannot reach. None of them is cured by trying again.