How to add Index to list items?

Hello Grist Team.
Contacts (table) can be:
NC (normaly close) with number 1, 2
NO (normaly open) with number 3, 4
ContactGroups(table) have more than one Contact Added by refList from Contacts
Is it possible to get the value of the contact number by formula like in column ContactGroups.Need:

1. get index No for Contact position in list $Scheme
2. get Contact number in this index
3. CONCAT index+1 and Contact number
4. Create List like in $ContactGroups.B but each contact Number must have his Index+1 in $Scheme column

I apologize in advance for this possibly confusing explanation.

I create this formula:

a = $Scheme.No
b = []
for i, ii in enumerate(a, start=1):
    for j in ii:

But i can`t find solution do it without adding using top level list.