Shape within the Heat map plot

Hello:

I want to plot heatmap of correlation matrix with significant cell value (p-value < 0.05) to be marked with a black symbol. While, I can plot heat map following this link: https://de.mathworks.com/matlabcentral/answers/88131-assigning-black-color-to-zero-values-of-imagesc-plot

I am looking something like this, shape within heatmaps: https://community.tableau.com/thread/172524

But instead of up/downward sign, I am looking for a circle indicating the cell with significant correlation. Can anyone please help, how to get so? Thanks