A scan can be started via tasker with a "run shell" command
Use the following line to run a scan:
am startservice -n gonemad.gmmp/.data.scanner.FileScanService -a gonemad.gmmp.filescanservice.auto_scan --ez show_notification true
or if you prefer adb
adb shell am startservice -n gonemad.gmmp/.data.scanner.FileScanService -a gonemad.gmmp.filescanservice.auto_scan --ez show_notification true