Please understand that we need information from you in order to help you.
"I'm struggling with my YouTube and gmail app." isn't helpfull. What exactly is the problem you're facing?
And which attemps you found online didn't help? Why didn't they help (e.g. did you get any error message)?
For huawei p9, you just need to download the Google Play Store apk from apkmirror or apkpure and sideload the Play Store app. Then you will find the launch icon of Play Store.
Open Play Store to install YouTube and gmail app.