The answer to 'how to unclog sump pump' is to first locate and remove the sump pump cover. Then use a wet/dry shop vacuum to suck out any debris or blockages in the sump pit. If that doesn't work, you may need to disassemble the sump pump to clear the impeller or intake screen. Make sure to unplug the pump before servicing it.
Unclogging a sump pump is a relatively straightforward maintenance task, but if you are not comfortable working with electrical equipment or can't identify the cause of the clog, it's best to call a professional plumber. They have the right tools and expertise to properly diagnose and fix the issue.