Hey there rahman74,
Thanks for reaching out to the Apple Support Communities.
To get started, we do want to make you aware that purchased ringtones would not show up in the 'Purchased' section of the iTunes Store app. For steps on how to set your ringtone as your default tone for calls or for a certain contact, as well as steps on how to redownload tones, check out this link here: Use tones and ringtones with your iPhone or iPad - Apple Support
Change your ringtone
1. Go to Settings > Sounds & Haptics.
2. Under Sounds and Haptic Patterns, tap the sound that you want to change.
3. Tap a ringtone or alert tone to hear it and set it as the new sound.
Set a ringtone or text tone for a contact
1. Open the Contacts app and tap a person's name.
2. In the upper-right corner of the person's contact card, tap Edit.
3. Tap Ringtone or Text Tone, then choose a new sound.
Redownload ringtones purchased with your Apple ID
1. Go to Settings > Sounds & Haptics.
2. Under Sounds and Haptic Patterns, tap any sound.
3. Tap Download All Purchased Tones. You might not see this option if you already downloaded all the tones that you purchased or if you haven't purchased any tones.
Let us know if that's able to help.
Have a great day!