Im trying to change my notes password

I think your notes are then lost.

Here

https://support.apple.com/en-us/HT205794

Apple says

If you forgot your notes password

You can unlock a note only when you enter the password that it's locked with. If you forgot your password, Apple can't help you regain access to your locked notes.

You can reset your password, but this won’t give you access to your old notes. It will, however, let you password protect any notes that you create from that point forward with the new password. This could lead to you having multiple notes with different passwords.

If you have multiple passwords, you can't tell which password you should use when you look at your notes in the Notes list. When you open a note locked by your old password but enter your current password, you'll see an alert that you entered the wrong password with a hint for your old one. If you then enter the correct old password, you get the option to update that note's password to your current one.

You can reset your notes password by following the steps below:

Change Notes your password

On your iPhone, iPad, or iPod touch:

1. Go to Settings > Notes > Password.
2. Tap Change Password.
3. Enter your old password, then enter a new password and password hint.

On your Mac:

1. Open Notes.
2. In the menu bar, choose Notes > Change Password.
3. Enter your old password, then enter a new password and password hint.
4. Click Change Password.

If you forgot your notes password

You can unlock a note only when you enter the password that it's locked with. If you forgot your password, Apple can't help you regain access to your locked notes.

You can reset your password, but this won’t give you access to your old notes. It will, however, let you password protect any notes that you create from that point forward with the new password. This could lead to you having multiple notes with different passwords.

If you have multiple passwords, you can't tell which password you should use when you look at your notes in the Notes list. When you open a note locked by your old password but enter your current password, you'll see an alert that you entered the wrong password with a hint for your old one. If you then enter the correct old password, you get the option to update that note's password to your current one.

Reset your notes password

When you reset your Notes password, it doesn't delete or change the password of your notes that are already locked. If you have a note that uses an old password, you can update it to the new password when you enter the old password, remove the old password, then apply your new password to the note.

On your iPhone, iPad, or iPod touch:

1. Go to Settings > Notes > Password.
2. Tap Reset Notes Password.
3. Enter your Apple ID password.
4. Tap Reset Notes Password again.
5. Enter your new password and password hint.

On your Mac:

1. Open Notes.
2. In the menu bar, click Notes > Reset Password > OK.
3. Enter your Apple ID password.
4. Click Reset Password.
5. Enter your new password and password hint.

Let us know how you get on.

http://osxdaily.com/2016/07/25/reset-notes-password-ios/