Extract the content of the zip file, double-click the "setup.exe" file to begin the installation, then follow the on-screen instructions.
Now connect your iPhone to your computer. Unlock your iOS device, and if prompted, choose to trust the device.
Open iTunes and enable iTunes Wi-Fi sync for your iPhone. Read this guide to find out how you can do it.
Now click the AltStore icon in the System Tray, click Install AltStore, then choose your iOS device.
Enter your Apple ID and password when prompted.
Within a few seconds, AltStore will be installed on your iPhone. Once installed, go to Settings > General > Profiles (or Profiles & Device Management), tap on the profile labelled with your Apple ID, then press the Trust button.
Now head to the next section to find out how to install apps with AltStore.
Launch AltStore. It will appear as an icon in the menu bar.
Click on the AltStore icon in the menu bar and select Install Mail Plug-in. Follow the on-screen instructions to complete the installation.
Once the installation is complete, restart the Mail app. Next, you have to enable the Mail plugin. To do so, click on Mail in the menu bar, then select Preferences.
Click Manage Plug-ins...
Enable the plugin named AltPlugin.mailbundle, then click Apply and Restart Mail
Now connect your iPhone to your computer. Unlock your iOS device, and if prompted, choose to trust the device.
If you're on macOS Mojave, open iTunes and enable iTunes Wi-Fi sync for your iPhone.
If you're on macOS Catalina, go to your iPhone's summary page in iTunes and enable Show this iPhone when on Wi-Fi. If you're not sure how to do this, then go to this link to read the guide
Now click the AltStore icon in the menu bar, click Install AltStore, then choose your iOS device.
Enter your Apple ID and password when prompted.
Within a few seconds, AltStore will be installed on your iPhone. Once installed, go to Settings > General > Profiles (or Profiles & Device Management), tap on the profile labelled with your Apple ID, then press the Trust button.
Now head to the next section to find out how to install apps with AltStore.
How to Install Apps with AltStore?
Head to our IPA Library to download the .ipa file of an app onto your iOS device. You can skip this step if you already have the .ipa file which you wish to install
Once the IPA file is downloaded, open the AltStore app on your device and go to the My Apps tab.
Press the + icon in the top left corner. A list of your downloaded IPA files will be displayed. Tap on the IPA file which you downloaded earlier.
If you're using AltStore for the first time, you'll be prompted to enter your Apple ID and password to begin installation.
AltStore begins installing the app. It takes a few minutes to complete the installation.
Once the app is installed, it will appear in the My Apps tab and you can open it from there or from the Home screen.
Apps last for 7 days and you can easily resign them from your device by going to My Apps in AltStore, then tap the "X days" button next to the app.