If you don't have access to the Atera management portal you can uninstall Atera manually. This is also useful if you have reinstalled Atera and it will not connect.
Either use these commands (The registry ones are the important ones if you have uninstalled Atera and Splashtop):
msiexec /x {EFB51F01-9805-4293-BB16-6F17EF4CEDF2} /qn
timeout /t 5 /nobreak >nul
sc stop AteraAgent > nul 2> nul
sc delete AteraAgent > nul 2> nul
taskkill /f /im TicketingTray.exe > nul 2> nul
REG DELETE "HKEY_CURRENT_USER\Software\ATERA Networks" /f > nul 2> nul
RMDIR /S /Q "%userprofile%\appdata\local\temp\TrayIconCaching" > nul 2> nul
taskkill /f /im AteraAgent.exe > nul 2> nul
taskkill /f /im TicketingTray.exe > nul 2> nul
taskkill /f /im AgentPackageMonitoring > nul 2> nul
taskkill /f /im AgentPackageInformation > nul 2> nul
taskkill /f /im AgentPackageRunCommandInteractive > nul 2> nul
taskkill /f /im AgentPackageEventViewer.exe > nul 2> nul
taskkill /f /im AgentPackageSTRemote.exe > nul 2> nul
taskkill /f /im AgentPackageInternalPoller.exe > nul 2> nul
taskkill /f /im AgentPackageWindowsUpdate.exe > nul 2> nul
taskkill /f /im AgentPackageSystemTools.exe > nul 2> nul
taskkill /f /im AgentPackageHeartbeat.exe > nul 2> nul
taskkill /f /im AgentPackageUpgradeAgent > nul 2> nul
taskkill /f /im AgentPackageProgramManagement > nul 2> nul
taskkill /f /im AgentPackageRegistryExplorer.exe > nul 2> nul
timeout /t 4 /nobreak >nul
REG DELETE "HKEY_CURRENT_USER\Software\ATERA Networks" /f > nul 2> nul
REG DELETE "HKEY_LOCAL_MACHINE\SOFTWARE\ATERA Networks" /f > nul 2> nul
REG DELETE "HKEY_CLASSES_ROOT\Installer\Products\4758948C95C1B194AB15204D95B42292" /f > nul 2> nul
REG DELETE "HKEY_CLASSES_ROOT\Installer\Products\10F15BFE50893924BB61F671FEC4DE2F" /f > nul 2> nul
RMDIR /S /Q "C:\Program Files\ATERA Networks\AteraAgent" > nul 2> nul
RMDIR /S /Q "C:\Program Files (x86)\ATERA Networks" > nul 2> nul