Hello @Vanvisa Anusri
Welcome to the Atlassian community.
Only a Project Administrator or the Jira Administrator can control the Notification settings for a project.
If you want to ensure you know about all issues that are assigned to you, you can create a Saved Filter to get a list of those issues. You can set up a Subscription to that Saved Filter to send you an email of the output on a schedule.
It will not be the same as receiving an email immediately when the issue is assigned to you, but that is the extent of what you can do if you are not a Project Administrator or a Jira Administrator.
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