You can find your individual Steam ID by following the steps below.
[View your Steam ID]
1. Log in to your Steam account
2. Click on your username (on the top right) and select 'View My Profile'
3. Your Steam ID will be displayed as a link at the top
e.g.) https://steamcommunity.com/profiles/7656119845*******/
4. Copy the 17-digit number from the link and submit your inquiry
If there is no link on your Steam profile, you will need to set it to be displayed.
[Setting Steam ID to be public]
1. Click 'View' (on the top left) and select 'Settings'
2. Select 'Interface' on the settings
3. Check the 'Show full URL in the address bar' option to enable it
4. Click 'OK' to save the settings
[Additional steps: For users who have previously set a custom URL]
1. Log in to your Steam account
2. Click your username (on the top right) and click 'View My Profile'
3. While viewing your profile, select 'Edit Profile'
4. Scroll down until you see 'Custom URL' and delete the profile URL you set
5. Scroll down and click 'Save'
6. After refreshing the page, please check if the Steam ID assigned to you is displayed in the profile URL.