You really do want to use awk for this. Use grep to return the entire line of a page or file that contains something you want to match. Use awk to divide a line into parts and then choose which part you want to return.

What you need to include is a delimiter (also known as a "field separator" and represented as the -F option) in your awk statement. A delimiter acts like a column divider — think of a comma in a CSV file as the column divider.

The syntax is:
/usr/bin/awk -F : '{ print $2 }'

After the awk command, add the -F option followed by whatever character or string of characters you want to use as your delimiter. In this case, it's the colon : . The colon is separating column 1 returned and column 2 first.last.

The number in the '{ print $2 }' piece of the command says which column you want to return.

The full command would look something like:
echo returned:first.last | /usr/bin/awk -F : '{ print $2 }'
first.last

Can you give sample output?

% string="returned:first.last"

% echo "${string}"

returned:first.last

% awk -F: '{ print $2 }' <<< "${string}"

first.last

I had to use a herestring for this but you could pipe to it probably. I just don't know what your output looks like. In awk you can specify a field separator with -F which is what I am doing

% echo "${string}" | cut -d ":" -f 2

first.last

The same thing in cut you can set the "delimiter" with -d and then pick which field you want with -f

also shell does this with built-ins if you want to get extra gray beard

% echo "${string#*:*}"

first.last