I’ve offloaded my garage band app once from then am unable to install it again

What happens when you try? Error message(s)?

App Store, iTunes Store, or other Apple services - If you can't connect

 Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

If necessary

Hard reset.        

Do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.      

If you tap View in App Store, can you download it?

See if anything here helps.

iPhone – Won’t activate.        

iPhone/iPad - No Service or Searching.        

For WiFi

Connect to Wi-Fi on your iPhone, iPad, or iPod touch

Troubleshooting Wi-Fi issues in IOS.    

You are welcome.

Is the SIM from your current carrier? If so, contact them for support.

 iPhone - How to unlock for use with a different carrier.