Usually, but not always, the styles in the TOC are set to 'Automatically Update' so all you need to do is put your cursor in one of the paragraphs in the TOC and click the bullets button. If the other instances of that style immediately show the bullet then your job is done.

If not, modify the style and choose the Format button in the bottom left to see the numbering option (which reveals the bullets option).

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Andrew Lockton
Chrysalis Design, Melbourne Australia