is it possible to process html to auto close tags with no close tags?

Question

i have this string

<div>
  <p><strong>Elem_A</strong>String_A2_2 <String_A2_2> asdas</p>
  <p><strong>Elem_B</strong>String_B2_2 String_B2_2</p>
</div>

and i want to covert it to

<div>
  <p><strong>Elem_A</strong>String_A2_2 <String_A2_2/> asdas</p>
  <p><strong>Elem_B</strong>String_B2_2 String_B2_2</p>
</div>

basically i want to autoclose any non html known tag , because i have problems with processing this html in htmlagilitypack as it changes the meaning of the html.