When you can't log into the Gmail account and it keeps showing you the incorrect username or password error. it means, something is wrong with the user credentials. so here are the guide to fix it on your device. 

1. first of all, you need to check the user id and password for your Gmail account. 

2. Go to the Google dashboard. here you need to make sure that the gmail servers are working fine without any interruption. 

3. Sometimes, Gmail users are unable to access the gmail account because of the browser or computer issues. so you need to clear the browser and other cache data. after that, you should try to access the gmail account again. 

once you will make these changes into the Gmail account. it should start working fine. if you are still dealing with the same problem, please visit: why can't I sign into the Gmail account?