Hi @vincent88live,
Welcome to the Microsoft Q&A forum.
I would like to provide you with the following information:
- Restore the letter “a”
- You can press Command + Z to undo the action and restore the letter “a”.
- Check the Replace settings
- First, please check whether there is a setting that replaces the letter “a” with a space.
Step 1: Press Command + ,
Step 2: Click AutoCorrect
- In the Replace section, look for the letter “a”.
- If there is a setting that replaces “a” with a space, please remove that setting.

- Check the Automatic Numbered List setting
- Next, please check the automatic numbered list setting.
Step 1: Press Command + ,
Step 2: Click AutoCorrect > AutoFormat As You Type
Step 3: check Automatic numbered lists

Additionally, if you want to apply numbering later, you can:
- Hold down the Command key, then select the lines or paragraphs you want to number.
- Next, click the Numbering button on the Home tab. Word will automatically apply numbering for you.

You can also choose the numbering style you prefer, for example:

I hope this information is helpful. Please follow these steps and let me know if it works for you. If not, we can work together to resolve this.
Thank you for your patience and your understanding. If you have any questions or need further assistance, please feel free to share them in the comments on this post so I can continue to support you.
I look forward to continuing the conversation.
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