What you are looking for are Linked product variations/ Combined listings. If you are on a Plus plan, Shopify has a specific app for it: https://help.shopify.com/en/manual/products/combined-listings
Otherwise, depending on the theme you are using, it could be a default feature, which would most likely require some configuration to be set. I’d recommend contacting theme support to check if your theme includes this.
If you are using a theme that does not have this feature, you’ll need an app for this. You’ll find some options in Shopify’s app store: https://apps.shopify.com/search?q=linked%20products%20combined%20listing