Although other forum members can ignore you, they actually can unignore you. You can focus on yourself, improve your post quality and they can by chance and curiosity unignoring you in future or you can proactivelly send them DM for a request of unignore your account. You must change yourself first before sending DMs for such request as it does not make sense when you are the same but want other forum members to change.

You can do this in DMs or in your thread in Reputation board if you strongly believe that your posting quality already changed and better enough.