Shopify has this covered!
1. Head over to Product > Collections.
2. Select the collection you want to edit the description of.
3. Scroll to the bottom. Click on Edit website SEO in the Search engine listing preview box.
4. Write a new description for that collection and save.
First of all, thank you for your answer. Unfortunately, following these steps only help to change the meta description of collections generated manually.
Shopify automatically generates a page '/collections' which isn't accessible anywhere on the dashboard. This auto-generated page takes the meta-description of the homepage, hence generating an SEO error for pages sharing the same meta description.
Could you please share a solution on how to change the meta description of this autogenerated page?