Want to put a allure floor over tile floor but have to fill in grout lines what do I use

Going to put down allure floor over tile floor but have to fill in grout lines. What do I use to do this

So you are laying the vinyl over a ceramic or some sort of tile, right?

Yes

"ceramic or some sort of tile" which one? Is the existing tile perfectly smooth?

So you are laying the vinyl over a ceramic or some sort of tile, right?

Yes

"ceramic or some sort of tile" which one? Please try to answer all parts of my questions.

"ceramic or some sort of tile" which one?? Is the existing tile perfectly smooth?

Ceramic and it is smooth

OK, I can tell you how to fill the grout lines but I will also suggest the finished product will not be as nice as you are hoping for. Fill the line with sanded grout and screet with a straight edged trowel. Do not wipe the grout like you do when grouting the first time. Here is the problem. Each tile is laid and appears to be perfectly smooth and level but they are not 100% level to each other. When the tile is first set the installer eyeballed the set and made it look good but by no means insure that every tile was true to the tiles next to it. You may luck out but I think most installers would recommend a new sub floor be installed