how to change the position of a suptitle() text in matlab

You can change the position of the suptitle() by setting the Position property of the title object. The Position property is a four-element vector in the form of [left bottom width height]. Here's an example:

main.m
% Create a plot
figure
plot([1 2 3], [4 5 6])

% Add a suptitle
suptitle('My Super Title')

% Get the title object
titleHandle = get(gcf,'NumberTitle', 'off');
titleHandle = get(titleHandle,'Name');
titleHandle = get(titleHandle, 'children');
titleHandle = titleHandle(1); % First title is the suptitle

% Change the position
set(titleHandle, 'Position', [0.5 1.05 0.5])
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In this example, the Position property is set to [0.5 1.05 0.5]. The 0.5 values for left and width center the title horizontally, and the 1.05 value for bottom moves the title slightly above the top of the plot.