Volume. for Audio clips

Highlight the portion you want to lower. Go to menu Process / Apply Effect / Gain. Change percentage or db in From Left and From Right to desired level. Click OK. There ya go!
 

Phoen1xPJ
Highlight the portion you want to lower. Go to menu Process / Apply Effect / Gain. Change percentage or db in From Left and From Right to desired level. Click OK. There ya go!
 

The only problem with that is.. its destructive editing (meaning its not reversible).
Automation doesn't permanently alter the audio clip.
 
I used to work this way all the time back in the day. Many classic artist did as well.
Think about some great albums made using processing on recorded tracks.
I guess now that we have the means to save our original work, it becomes money in the bank.
Allowing clips to be brought back to its original recording.

Alan-Russell
I was able to UNDO to do any Left Right percentages in the Gain while working on the track to acheive the desired volume.
it was quite easy

That's fine whilst your project is still open and held in RAM
Once you close it however, you lose the ability to undo anything
Please, check out the links on automation, it's really the only way to go

Alan-Russell
I totally understand the automation procedure that’s why I have back up files

Just to question,, but really make the case for'. Why not use either track automation (with the avoidance of messing with any track dynamics threshold that may be in use), or clip automation (which is pre-track insert, like the 'apply clip gain function, but also totally flexible?
 

Both methods = applying gain and automation get you to the same place and each has merits. 
 
As said the quick and easy use of a volume envelope is simple and non destructive. You don't like the results, no problem drag the node to fix.
 
But then volume envelopes have a down side when you start chopping songs up and moving things around. 
 
Often the reason a vocal part is at a different level was a mistake made will tracking. Say a punch in and the singer moved further away from the mike. 
 
If it's only a short section you'll often actually "see" the difference in level when looking at the waveform. 
As the OP said, they have back ups so there is no real reason not to perform a gain rendering to that little section.  
You dial in the the amount needed to level that part with the rest and render and forget about it. It's done. No messy envelopes. And the word destructive is misleading. We are rendering at 32 bits.. I dare anyone to find anything that's been destroyed. 
 
Now you slap an compressor in the bin and push the vocals and all will be nice and even.