Thank you for contacting the World Warfare support team.
We are here to answer any questions or concerns you may have on how to repair any damaged units.
To refill troops within your army/naval/air force base, you need to order any troops that need repairing to enter one of the above mentioned bases. To do this, simply select the damaged troops and choose "Enter" and select the appropriate base as a target. Note that there is a timer here while the troops are entering that base so please be patient.
Once you have the selected troops within an assigned base, you then select your base and choose "Troop List" to refill them.
Be sure to select the unlock button for the "auto dispatch" box in case your troops are immediately dispatched. Additionally, you will need to unlock the refill function by increasing all bases to lvl 3.      
When using tactics to refill troops, note that some tactics such as "Persuade Captive" and "Life Saving" can also restore your troops' power.
Fortune and population is needed to refill troops. If your troops are heavily injured, extra armament is required.

We hope to have been able to assist you and please do not hesitate to contact us again!