For Langify V1
langify adds hreflang tags as soon as you separate your languages by (sub)domains as described in this guide: Enabling the domain feature.
For Langify V2
In the new version, the hreflang tags are managed by Shopify itself. If you still have the code from v1 in the theme, you have to delete it or ask the support at email@example.com
Please make sure to validate your hreflang tags here.
This is how it should look like: