How to modify hreflang for specific site

Hi team,

I am glad to find this useful plugin. When setting this plugin in my sites, I met an issue about the hreflang. There are total 4 sites in my WordPress multisite. All of them are in English but for different countries. To have the site target the corresponding countries, I would like to set hreflang as below.

• International site – en
• Singapore site – en-SG
• UK site – en-GB
• Australia site – en-AU

For the UK site and Australia site, I can change hreflang by setting the site language. However, for international site and Singapore site, there is no option in the site language list. Their hreflang tags are en-US.

I tried to use the snippet in the hook reference (https://msls.co/developer-docs/hook-reference/) to modify the hreflang tags. However, due to my limited knowledge, I could not change the hreflang tag for specific site only. Would it be possible to suggest me how to change it?

Best regards,

Lin