Hi Megha,
The font size of the Tool Tip string within the Property Inspector is related to the operating system settings and hence there is not much control on them. Please have a look at the following MATLAB Answers for more information: https://www.mathworks.com/matlabcentral/answers/225624-can-i-change-the-font-size-of-the-toopltipstring-in-property-inspector-gui
However, if your goal is to increase the font size of the tool-tip string for some UI object within a figure, you can use HTML as the string value to modify the tool-tip appearance. As an example, the font size and color of tool-tip string for a pushbutton can be modified as follows:
>> str = ['<html><center><b><font color="red" size="20"> HELLO']; %HELLO is the text message to display
>> set(pushbuttonObject, 'tooltipString', str);
Hope this helps.
Cheers!
