if you have a text like:

3h3s2h2s
3d3h2h2s
3c3h2h2s

open up the notepad++ menu search > replace and enter the following:

search what: ([0-9][a-z])
replace with: <img src="$1.png">
search mode: regular expression

then either hit replace to replace every occurrence one by one,
or hit replace all to parse-replace the complete file.

note: if you have similar conflicting content in your file, select only the part you want to parse-replace and activate in selection before you hit replace all.

the result will then be:

<img src="3h.png"><img src="3s.png"><img src="2h.png"><img src="2s.png">
<img src="3d.png"><img src="3h.png"><img src="2h.png"><img src="2s.png">
<img src="3c.png"><img src="3h.png"><img src="2h.png"><img src="2s.png">

if your result differs, we would need a real life example of a part of your file.

best regards.