This goes back to my previous reply where I presented an assumption that your servo only needs a signal, variable from -10V to +10v with respect to a common ground. So, one signal, capable of any voltage between -10V..+10V. For that, a single Op-Amp, the output of which is connected to the servo, and the other servo input connected to ground.

It's possible, though without any literature we have no means to corroborate, that the servo requires a differential drive - with one signal increasing from 0..+10V, whilst the other input decreases from 0..-10V, in which case you certainly would need 2 op-amps, or a specialised op-amp that provides the differential drive. Such a signalling regime is good for noise immunity.

Can you offer any of the literature that you have for the servo just so we can be certain of the advice offered?