How to merge 3 old existing SKU into 1 new subscription in Play Console?

Before we had 3 different SKUs in Play Console for the app. But with Recent changes to subscriptions in Play Console and the Billing Library 5.0, the concept of SKU is considered deprecated. And the docs say the following:

"When this functionality launched, any existing subscriptions were converted into the new model. The results are:

• Each subscription now has a single base plan with the old subscription’s billing period. As prepaid plans didn’t exist, these
  base plans are all auto-renewing.
• Any free trial or intro price was converted into an offer".

And our 3 old existing SKUs (SKU A, B, C) were automatically converted into 3 different subscriptions, each with 1 base plan and 1 offer. But logically they would be merged into 1 subscription, with 2 base plans and 3 offers: So the question is whether we should make changes in Play Console to merge these existing SKUs into 1 subscription (with 2 base plans and 3 offers) or if we can simply treat 3 old existing SKU as 1 new subscription via the new Billing Library 5.0 API without any changes in Play Console. And if we should make changes in Play Console to merge these SKUs into 1 subscription, then how to do this?

Unfortunately you won't be able to treat 3 old SKUs as 1 new subscription without any changes. They will be a separate products (ProductDetails items).

I'd suggested to leave old SKUs as is for backward compatibility and then to create a new Subscription with base plans and offers. Since implementation of new approach will likely require significant changes.

For example, instead of single SkuDetails per SKU with all data on reccurence, price etc. you'll need to work with new ProductDetails which will contain list of SubscriptionOfferDetails. Where each base plan and each offer will be a separate SubscriptionOfferDetails item. And each such item will contain 1 or more PricingPhase items (depending on offer setup) with all the details on price, duration and recurrence.