I mean the torrent was downloaded(59%) by Transmission and now I want to complete the download from Tixati but starting from 59%!

As in every other torrent client, you'll need the original torrent file. Add torrent to Tixati and point into the folder with the partially downloaded content.

First make sure the previous client didn't add a filename extension (Like an incomplete filename extension option) if so remove it. If this is multiple files check all of them.

Second load up the torrent file or magnet link in Tixati and point the download location to folder that has the file/folder that is already downloaded, Tixati should check it and continue.

No its not working! :(

You're asking for too much.
Every torrent client has its own file system.
To get what you're asking for would require all the different torrent clients to use an interchangeable file system.
It'll never happen.
You'll have to either finish the partial download with the old torrent client or start it over with the new client from the beginning.

Just saying it does not work is not worth a reply, but I guess I am patient this morning. What steps did you do and what has failed? Let me assure you it does work, I do it frequently. I also move files between torrents to get them to complete.

I will give you a new way, that works safely because sometimes people over write the file and they have to start the download from new.

First don't move the file to the directory that you want to download in, only do that after the torrent has written the new file.

Open your torrent and select the files and directory ETC. Click start and let the files be written and then stop the torrent.
Open explorer and drag the file you have to the new download directory and drop. You should get a warning from windows about the file existing and you are about to overwrite, if you don't you have a naming issue. This likely means you don't have the correct torrent, but that might be ok anyway. Correct the name issue. I most often do this by simply going to the new directory and open the new file for renaming copy it's name then add a 1 to the beginning . I then rename my existing file by choosing paste.

Now go back to tixati and start the torrent and tixati will auto check the file and finish your torrent. If you get a warning that the file is the wrong size or it appears to be much less complete (expect that you can lose 2 pieces)than what you remember then you have downloaded the wrong torrent. If it shows less complete that is usually caused by different torrent makeup in piece size or which file is first.

As I said I use this frequently for completing torrents that will not complete and it works very well. By moving a file around to two or more torrents you can get it complete and seed to complete the torrents you had to use.

If you do that try and seed those torrents for a couple of weeks because the peers that were partly complete will likely auto off because many people have downloaded from them and they will have seeded more than their ratio. The people you seed later will have a smaller ratio and the torrent will likely survive.

Sailor24's method above works.