And from now on, after the initial conditioning (fully charge* the tab, let it run until it turns off [you don't have to leave it on, you can turn it off and on as you need it, but don't charge it again until it turns off], then fully charge it), try to never let it get below 40%. Lithium batteries don't do well if they're deep discharged. (I have 11 year old batteries that are still working.)
*"Fully charge" means let the phone reach 100%, then leave it on the charger for 30 minutes. Due to the way state of charge is measured**, at the moment the phone indicated 100%, it's about at 98%. The 30 minutes lets it charge up the additional 2%.
**SoC is measured by the voltage at the battery terminals. To charge the battery, the charging voltage has to be higher than the battery voltage, to "push" current into the battery. When the battery reaches about 98% charge, the charging voltage is about the voltage that should be across the battery terminals for 100% charge, so the phone indicates 100%. (The charging circuit turns off when the battery is actually 100% charged, so leaving it on an additional 30 minutes - or 30 days - won't harm anything.)