First try to create a new phrase
AdimnCP > Language & phrase >phrase manager >Add new pharse
Phrase Type
Product: vBulletin
Varname: members_id
Text: Members id
Then save it!
Then in your postbit_legacy Find this code
Code:
<dl class="userinfo_extra"
Add this code below!!
Code:
<dt>{vb:rawphrase 'members_id'}</dt>
<dd>{vb:raw post.userid}</dd>
Thanks to Gunit1000