Hi @Ree_81 !
Zac is correct in what he’s saying - if you add a new subdomain this will not reset your deliverability score. Your deliverability score and sender reputation are attached to your root domain, not your sub domain. If you wanted to “reset”, you would need to create a new branded sending domain entirely and then go through warming for that domain. The warming process is outlined in further detail here: https://help.klaviyo.com/hc/en-us/articles/360025945671#h_01HFA4HFQTPA3JKWA2WY1SEJF8 .
Essentially, if you just changed your subdomain, inbox providers can connect the dots back to your root domain reputation and will go based off of that.
Here is our guide for repairing your sender reputation if you decide to stick with the same domain: How to repair your sender reputation
I hope this helps clarify!