Struggling to differentiate the 'th' and 'dh' sounds in Arabic loanwords

I’ve been practicing my Swahili pronunciation for months, but I constantly hit a wall with loanwords like 'dhahabu' or 'thelathini'. I record myself daily, but I can't tell if I'm hitting that dental fricative correctly or just defaulting to an English 'th'. Any tips on tongue placement for these sounds specifically for a non-native speaker?