I think about how to add a from lookup value to the text ? How can I write it to another colum ? In the same list.
You can extend the ID column into the Child List from Lookup Fields... If you go to Site Settings -> Click lookup Column -> In section "Add a column to show each of these additional fields" check ID field!
Then in code you can access it like:
Replace "LookupListName" with the Lookup List's name in your case!
Now when you access the fields in code, you need to use Internal Names and all the special characters are replaced by some code... code for ':' is 'x003a', so when you try to access the field in code you will write:
You can see complete code conversions here:
If I have understood the question correctly...