The default font size of messages in Telegram may be too large or too small for you, making them uncomfortable to read. Fortunately, you can easily adjust your message text size. Just follow the steps listed below.
1. Tap the hamburger icon on the top left of the screen to open the drawer menu then select Settings:
2. Go to Chat Settings:
3. Now you’re on the Chat Settings page. To decrease or increase the font size of messages, just move the thumb of the slider left or right, respectively. See the screenshot below for more clarity: