***Help*** allows both a plain infinitival complement and a *to*-infinitival complement when it's a verb. The *-ing* clause as complement is marginally acceptable at best. 

In the [Corpus of Contemporary American English][1] the results for 'he helped...' are as follows:

 - plain infinitival 329
 - *to*-infinitival 232
 - *-ing* clause 2

Only one of the *-ing* clause examples could actually be argued as a complement to ***help***.

> Snape's logic and deductive reasoning skills were such that he **helped
> protecting** the Philosopher's Stone by creating an obstacle ([Harry
> Potter Wiki][2])

The Cambridge Grammar of the English Language has verb ***help*** on p1229 as  allowing *to*-infinitivals and bare infinitivals, but not gerund-participials (*-ing* clauses).

Then again, [ngrams][3] gives 'help adding' as quite a common colocation, more so even than 'help add' or 'help to add':

[![ngram of 'help add', 'help to add', 'help adding' showing that 'help adding' is more common than the other two][4]][4]

However, most of these hits are noun uses.

In fact, when a noun, ***help*** can be followed by -*ing* clauses. The string 'some help *doing something*' returns 251 hits in the Corpus of Contemporary American English. These are quite acceptable:

> Want some help finding that dog?
> 
> I knew you'd need some help keeping it real.
> 
> Maybe he'd like some help cleaning it out.

Then there's also ***can help*** in non-affirmative contexts which only licenses *-ing* clause complements (CGEL p1232) as in *No one can help liking her*. These make up the vast majority of hits for 'can help doing something' in the Corpus of Contemporary American English.

In the sentence given though, ***help*** is quite definitely a verb, and used in an affirmative context, so it would be best to have either a plain infinitival or *to*-infinitival following it.

---

Another possibility, as others have mentioned, is the solution of adding a ***by*** before the *-ing* clause to make it an adjunct of means, which in this case may be preferable if the person helping is in fact adding all of them; however, helping add them, or helping to add them by adding some but not all, is also perfectly possible.


  [1]: https://www.english-corpora.org/coca/
  [2]: https://harrypotter.fandom.com/wiki/Severus_Snape
  [3]: https://books.google.com/ngrams/graph?content=help%20add%2C%20help%20to%20add%2C%20help%20adding&year_start=1800&year_end=2019&corpus=en-2019&smoothing=3
  [4]: https://i.sstatic.net/pB1Bhovf.png