allowing them either to insert or remove mutations?

allowing them either to insert or remove mutations = allowing the ZFNs either to insert into mutations or or remove from mutations?

That is, " allowing them either to insert or remove mutations" means "the first method allows ZFNs insert the mutations to make the mutations normal, or, the first method allows ZFNs remove themselves (ZFNs) from the mutations to make the mutations normal?"

Context:

Precision Gene Targeting in Stem Cells Corrects Disease-Causing Mutations

ScienceDaily (July 27, 2011) — Using two distinct methods, Whitehead Institute researchers have successfully and consistently manipulated targeted genes in both human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells (adult cells that have been reprogrammed to an embryonic stem cell-like state).

In one case, scientists employed proteins known as zinc finger nucleases (ZFNs) to change a single base pair in the genome, allowing them either to insert or remove mutations known to cause early-onset Parkinson's disease (PD). The second method relies on proteins called transcription activator like effector nucleases (TALENs) capable of altering specific genes with similar efficiency and precision as ZFNs. Both sets of experiments were conducted in close collaboration with scientists at Sangamo BioSciences.
Targeted genetic manipulation addresses a problem that has been plaguing human stem cell research -- the ability to cleanly and site-specifically modify the genomes of human ES and iPS cells. Realizing the therapeutic promise of these cells depends on such changes to fix disease-causing mutations before the cells could be transplanted into patients or to create cell lines that researchers can use to study genetic diseases.