STM32 sim 7500 module
In the SIM75XXX hardware design document, Page 19, an interface introduced, which is probably the answer to your problem (it changes the state of PWRKEY to high):



And if you can not reset the module with making the PWRKEY pin state to high, Try the the emergency solution, which is explained on page 21 of the same document (AKA changing the state of RESET pin to zero):



PS. Read the datasheets!