Linking figure caption number to chapter number in a different style than Heading 1 in Word

I am using a customized thesis template where the styles are manually created. However, there are no standard Word styles, such as "Heading X." I am trying to include chapter numbers in my figure captions. While attempting to do so, I've selected include chapter number in the Caption Numbering settings. Unfortunately, I encountered an issue; the Chapter starts with style cell only displays standard Word styles (Heading 1-9). It doesn't show styles other than Heading X. Consequently, I am unable to add chapter numbers in front of my figure numbers with my Chapter style (let's say "Title1") within the captions. Can anyone provide guidance on how to accomplish this?

I checked the multilevel list in the Home tab and looked through modifying the style.

When you open the Caption Numbering window, you cannot access any style other than Windows' own standard styles (Heading X) under Chapter starts with style. I was able to find a solution as follows: After writing a title with the style I created and wanted to use, I opened the Styles window with this style selected as the style type. Here, when I clicked on the downward arrow next to Heading 1, then I selected Update Heading 1 to Match Selection from the menu that opened. So, I copied the content of the style I created to Heading 1. In this case, if you select Heading 1 when you want to add the Chapter number, it links figure caption number to related chapter number successfully.