[Baertram]

I don't know such a tool but if you use some good and free text editor, like Notepad++, you would be able to see the SavedVariable file contents more clearly.

The { and } would build blovks that you can close and open by clicking the - and + symbols next to it.
If I remember right you can even jump from the opening { to the closing } by help of keybindings.
This way you can see which part belongs together.

If you just want to delete old character settings you need to find the character's name inside the file first.
An example file will look like this e.g.:

ExampleSavedVars =
{
    ["Default"] =
    {
        ["@AccountName"] =
        {
            ["YourOldCharacterName"] =
            {
                ...
            } -- closes YourOldCharacterName
 
            ["YourCurrentCharacterName"] =
            {
                ...
            } -- closes YourCurrentCharacterName
 
        } -- closes @AccountName
    } -- closes Default
} -- closes ExampleSavedVars

You can search for "YourOldCharacterName" and everything that is in between the opening { and the closing } after that username is the saved settings part for this character.

So if you use a good text editor, click the - symbol after your old character name and then select (by mouse or keyboard SHIFT+Key down) the line "YourOldCharatcerName" + the minimized { ... } block you are able to delete the whole block at once.

Account wide settings:
There are also some account wide settings which apply to each character! You can change them but deleting them will remove the settings for all your characters!
They look like this:

Example_AccountWide_Settings =
{
    ["Default"] =
    {
        ["@AccountName"] =
        {
            ["$AccountWide"] =
            {
            } -- closes $AccountWide
        } -- closes @AccountName
    } -- closes Default
} -- closes Example_AfccountWide_Settings