How to charge lipo with a laboratory power supply?
A direct way of doing it is to first analyze the battery and find its C rating. Then set the current limit of the power supply to under C/10, to be safe. So for say 2600 mAh battery, the limit should be under 260 mA. 

Next step is to get the charged voltage of the battery. For lithium batteries, that's 4,2 V per cell. You have a 3 S battery, so 3 cells in series, giving you 12,6 V. Set the voltage on the power supply to that value. Check it at the output with a good voltmeter, if you have one, just to be safe, since LiPo batteries don't like over-voltages.

Next step is to connect the battery to the power supply with an amperemeter connected in series in series. If your power supply already has an ampmeter, then you can use that. 

You need to watch the meter and wait for the current indicated on it to drop down to zero. When it's zero, the battery is fully charged. 

Do keep in mind that some LiPo batteries have special connectors for balancing cells. If your does have that, it would be a good idea to use a charger that can make use of that connector.