Can anybody help me in letter sample for a journal asking for permission to use figures in the paper?
Just ask. State clearly what paper the source is, who the authors are, which images are of interest and why. Explain what the use of the images will be, where you plan to publish the result. Ask for the exact way in which you should acknowledge the source.

As stated in comments, if the source of the images is your own paper or thesis, you'd need to check the agreement to publish those.

Make sure you cite the original source (your thesis, in this case) correctly.