Hold simultaneously. You should see the TWRP blue splash screen.
Use TWRP 2.8.7.0 for MT6592:
Turn off your phone. Open SP Flash Tool, load the "Scatter File" from the TWRP package. Uncheck everything except "RECOVERY." Click "Download" and connect your powered-off phone via USB. The tool will flash the custom recovery. huawei g750-u10 android 7