First, uninstall the Grammarly app from your device:
- Touch and hold Grammarly’s companion app.
- Tap Remove App.
- Tap Delete App and then tap Delete to confirm.
Once that's done, visit this page and click Install next to the Grammarly listing to download the app on your device.
When the app is installed, open it and click Get Started. If you already have a Grammarly account, tap Log in to existing account and enter your login credentials. If not, tap Continue with email to create an account.