E-Ink External Manipulation
If you are not contacting the original electrodes, you are probably facing the problem, that the upper invisible electrode an the bottom electrode form a sort of Faraday cage. It could also be that there is another layer especially for shielding integrated.

This will negate the electric field you are applying from the outside to be effective over the bubbles. Without an electric field the charged particles won't move.

Or it is just that your field is not strong enough. The driving voltage for E-Ink displays is +/- 15 V (for fast reaction). That is applied pretty much directly over the bubble, so the field strength is rather high. You might want to increase the voltage and the exposure time. E-Ink displays can be driven with lower voltages (+/- 5 V) but then it takes significantly longer to move the particles.