Hi @smileface,
Thank you for your post !
It requires to download TeamViewer application on both local and remote devices, if you haven't done that.
Are you new to TeamViewer??? - you can download the TeamViewer latest version from here.
Also, it would be great to check our knowledge article -Get started - For personal usage.
If your are using mobile device, a required application is different on local device and remote device.
For more information, please kindly check the knowledge article - Connections From Mobile to Mobile Devices.
Hope this could help.
If there is anything we may help further, feel free to contact us again.
Best Regards,
Akiho