Numbering per item

[numfon_naka]

In the item box, I want to sort the numbers.

is in the app is 2 tables
The first table is named head.
The second table is named PR (REF goes to the Head table).

In tabular templates, item up to LAST STOCK is the data in the in-app PR table.

I want it to be numbered list.

want to sort numbers
1
2
3
per item or that ID

in-app information

[Suvrutt_Gurjar]

You can use the INDEXOF() expression tip suggested by @Steve 

INDEXOF() - Google Cloud Community

So your Item Number expression in the template can be something like below

<<COUNT(
SPLIT(
ANY(
SPLIT(
(" , " & [Related PRs] & " , "),
(" , " & [PR Table Key Name] & " , ")
)
),
" , "
)
)>>

Here [Related PRs]  is the reverse reference column in the Head Table and  [PR Table Key Name] is the key column of the PR table.