Palaan palvelutiskille, jos leima puuttuu tästä paperista.

Palaan is the 1st person singular present tense form of the verb palata (to return / to go back).

• palata → palaan = I return / I’ll go back (Finnish present can often cover near-future intent as well, depending on context).

Finnish usually doesn’t need subject pronouns because the verb ending shows the person.

• palaan already means I
  • return, so minä palaan is optional and would add emphasis/contrast (like I (as opposed to someone else) will return).

-lle is the allative case, commonly used for movement to a place (especially “onto/to the vicinity of”).

• palvelutiski = service counter/desk
• palvelutiskille = to the service counter

They are different location/movement cases:

• palvelutiskille (allative) = to the counter (destination)
• palvelutiskissä (inessive) = in/at the counter (location)
• palvelutiskiltä (ablative) = from the counter (origin)
  So the sentence uses -lle because it’s about going back to the counter.

jos means if and introduces a conditional clause. Finnish normally separates that clause with a comma.

• Main clause: Palaan palvelutiskille
• If-clause: jos leima puuttuu tästä paperista
  Comma use is standard in Finnish when an if/when/because-type subordinate clause is attached.

Finnish often expresses “X is missing (from Y)” using puuttua:

• leima puuttuu = the stamp is missing
  It’s not phrased as “I miss…” but as a state: something is missing.

puuttua typically takes the elative case (-sta/-stä) to mark where something is missing from.

• puuttuu tästä paperista = is missing from this paper/document
  This is a common verb + case pattern you mostly learn as a chunk: puuttua jostakin = to be missing from something.

With puuttua, the thing that is missing is commonly in the nominative when it’s treated as a specific item:

• leima puuttuu = the stamp is missing
  You can see partitive in some contexts (often when meaning is more “some amount is lacking”), but for a single missing stamp, nominative leima is the normal choice.

tästä is the demonstrative tämä (this) in the elative case (from this).

• tämä paperi = this paper
• tästä paperista = from this paper
  It matches the verb pattern puuttua jostakin.

Yes. Both are natural, with only small differences in emphasis:

• Palaan palvelutiskille, jos leima puuttuu tästä paperista.
• Jos leima puuttuu tästä paperista, palaan palvelutiskille.
  Starting with the jos clause can feel slightly more like setting the condition first (very similar to English).