I found the PowerShell script which will update the profile picture of Delve user in SharePoint Online from here.
The script is:
$UserCredential = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/?proxyMethod=RPS -Credential $UserCredential -Authentication Basic -AllowRedirection
Import-PSSession $Session -AllowClobber -WarningAction SilentlyContinue -ErrorAction SilentlyContinue
$user1 = ([Byte[]] $(Get-Content -Path C:\1\Tomek1.jpg -Encoding Byte -ReadCount 0))
set-userphoto -identity user@domain.anme -picturedata $user1
Remove-PSSession $Session